Direct methanol fuel cell system, fuel cartridge, and memory for fuel cartridge

ABSTRACT

A fuel cartridge to be connected to a direct methanol fuel cell power generating device includes a spare fuel tank which stores a liquid fuel and is to be connected to the direct methanol fuel cell power generating device and a harmful substance trap member. The spare fuel tank stores a liquid fuel and is to be connected to the direct methanol fuel cell power generating device. The harmful substance trap member is fixed to the spare fuel tank and is to be connected to the direct methanol fuel cell power generating device. The harmful substance trap member contains a harmful substance trap material which traps gaseous harmful substances exhausted from the direct methanol fuel cell power generating device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 USC § 120 from U.S. patent Ser. No. 11/936,911, filed Nov. 8,2007 which is a continuation of U.S. patent Ser. No. 10/458,299, filedJun. 11, 2003, which claims the benefit from the prior Japanese PatentApplications No. 2002-171520, filed Jun. 12, 2002; No. 2002-260762,filed Sep. 6, 2002; and No. 2003-061872, filed Mar. 7, 2003, the entirecontents of all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a direct methanol fuel cell systemcapable of driving electronic appliances hitherto using a battery asdriving power source such as small portable appliances.

2. Description of the Related Art

Recently, fuel cells have high expectations as a power source for use inportable electronic appliances supporting the age of informationtechnology, or as measures against air pollution and global warming.

Of the various fuel cells, the direct methanol fuel cell (DMFC) forgenerating power by taking out protons directly from methanol hasoutstanding benefits, such as no need of a reformer, and small fuelamount, and its application in portable electronic appliances is beingdeveloped. It is thus expected to be applied in many fields.

As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-93551, acontainer for holding a liquid fuel of a direct methanol fuel cell isdetachable, or is capable of being replenished with liquid fuel, anddriving for a long period is realized while reducing the size of thefuel cell.

This type of direct methanol fuel cell is required to control theconcentration of the methanol aqueous solution supplied as fuel, but theoptimum concentration varies according to the load, which fluctuates,and the amount of the replenished methanol. The correct-supply amount inrelation to an external load is not known unless actually operated for along time, thus a practical direct methanol fuel cell capable ofgenerating power stably for a long period has not been developed yet.

BRIEF SUMMARY OF THE INVENTION

The present invention is devised in the light of the problems of theconventional DMFC system, and it is hence an object thereof to provide apractical direct methanol fuel cell system capable of stably supplyingelectric power to a load over a long period, a fuel cartridge, and amemory for fuel cartridge.

According to a first aspect of the present invention, there is provideda direct methanol fuel cell system comprising:

a power generating unit which includes an anode electrode, a cathodeelectrode, and an electrolyte layer provided between the anode electrodeand the cathode electrode;

a characteristic-measuring mechanism which measures one characteristicof a voltage characteristic and a current-voltage characteristic in thepower generating unit; and

an external load supply mechanism which supplies an electric power ofthe power generating unit to an external load on the basis of the onecharacteristic.

According to a second aspect of the present invention, there is provideda direct methanol fuel cell system comprising:

a power generating unit which includes an anode electrode, a cathodeelectrode, and an electrolyte layer provided between the anode electrodeand the cathode electrode;

a variable resistor;

a resistor which detects a current flowing into the variable resistorfrom the power generating unit;

a voltage detection mechanism which detects a voltage of the powergenerating unit when the current flows in the variable resistor; and

an external load supply mechanism which supplies an electric power ofthe power generating unit into an external load on the basis of acurrent-voltage characteristic.

According to a third aspect of the present invention, there is provideda direct methanol fuel cell system comprising:

a power generating unit which includes an anode electrode, a cathodeelectrode, an electrolyte layer provided between the anode electrode andthe cathode electrode, an anode fluid channel which supplies methanolaqueous solution to the anode electrode, and a cathode fluid channelwhich supplies air to the cathode electrode;

a liquid supply mechanism which supplies methanol aqueous solution tothe anode fluid channel;

an air supply mechanism which supplies air to the cathode fluid channel;

an auxiliary power source which drives the air supply mechanism and theliquid supply mechanism;

a variable resistor;

a resistor which detects a current flowing into the variable resistorfrom the power generating unit;

a voltage detection mechanism which detects a voltage of the powergenerating unit when the current flows in the variable resistor;

an external load supply mechanism which supplies an electric power ofthe power generating unit into an external load on the basis of acurrent-voltage characteristic; and

a changeover mechanism which changes over between the auxiliary powersource and the power generating unit on the basis of the voltage of thepower generating unit.

According to a fourth aspect of the present invention, there is provideda direct methanol fuel cell system comprising:

a power generating unit which includes an anode electrode, a cathodeelectrode, an electrolyte layer provided between the anode electrode andthe cathode electrode, an anode fluid channel which supplies methanolaqueous solution to the anode electrode, and a cathode fluid channelwhich supplies air to the cathode electrode;

a characteristic-measuring mechanism which measures a current-voltagecharacteristic of the power generating unit;

an external load supply mechanism which supplies an electric power ofthe power generating unit to an external load on the basis of thecurrent-voltage characteristic;

a methanol aqueous solution container which stores methanol aqueoussolution to be supplied to the anode fluid channel; and

a fuel cartridge which stores methanol aqueous solution to bereplenished in the methanol aqueous solution container.

According to a fifth aspect of the present invention, there is provideda fuel cartridge for supplying methanol aqueous solution to a directmethanol fuel cell system, comprising:

a memory which stores at least a concentration of the methanol aqueoussolution.

According to a sixth aspect of the present invention, there is provideda memory for fuel cartridge for use in a direct methanol fuel cellsystem that comprises a container and a fuel cartridge from whichaccommodates methanol aqueous solution is to be supplied into thecontainer,

wherein the memory is fixed in the fuel cartridge, and a firstinformation about the fuel cartridge, or a second information about themethanol aqueous solution is stored the memory.

According to an seventh aspect of the present invention, there isprovided a direct methanol fuel cell system comprising:

a power generating unit including an anode electrode, a cathodeelectrode, and an electrolyte layer provided between the anode electrodeand the cathode electrode;

a fuel tank which stores a fuel containing methanol; and

a fuel cartridge comprising a spare fuel tank which stores a fuel thatcontains methanol and is to be replenished in the fuel tank, and aharmful substance trap member which traps harmful substances in a gas inthe fuel tank.

According to a eighth aspect of the present invention, there is provideda fuel cartridge to be connected to a fuel tank of a direct methanolfuel cell, comprising:

a spare fuel tank which stores a fuel to be replenished in the fueltank; and

a harmful substance trap member which traps harmful substances in a gasin the fuel tank.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram showing a structural example of a DMFC powergenerating device for use in an embodiment of the invention.

FIG. 2 is a diagram showing a circuit configuration example of theembodiment of the invention.

FIG. 3 is a diagram for explaining the current-voltage characteristic inthe embodiment of the invention.

FIG. 4A is a diagram explaining another configuration example of an IVcharacteristic measuring unit in the embodiment of the invention.

FIG. 4B is a diagram explaining another configuration example of an IVcharacteristic in the embodiment of the invention.

FIG. 5 is a flowchart for explaining the operation in the embodiment ofthe invention.

FIG. 6A is a diagram for explaining another embodiment of a methanolaqueous solution container and a fuel cartridge in the invention.

FIG. 6B is a diagram for explaining another embodiment of a methanolaqueous solution container and a fuel cartridge in the invention.

FIG. 7 is a schematic diagram showing an example of another directmethanol fuel cell system according to the invention.

FIG. 8 is a perspective view schematically showing an example of aharmful substance trap member of the direct methanol fuel cell system inFIG. 7.

FIG. 9 is a cross sectional view showing a gas diffusion path of theharmful substance trap member in FIG. 8.

FIG. 10 is a perspective view schematically showing another example ofthe harmful substance trap member of the direct methanol fuel cellsystem in FIG. 7.

FIG. 11 is a diagram explaining one configuration example of a variableresistor in the embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It is a feature of the invention that the voltage or current-voltagecharacteristic of electric power generated by a power generating unit ismeasured so that the electric power is supplied to an external load onthe basis of the characteristic.

In order to achieve the object, the invention provides a direct methanolfuel cell system comprising a power generating unit which generateselectric power by chemical reaction between a methanol aqueous solutionthat is a fuel and passes in an anode fluid channel and air that is anoxidizer and passes in a cathode fluid channel, characteristic-measuringmechanism which measures the voltage or current-voltage characteristicof the electric power generated in the power generating unit, andexternal load supply mechanism which supplies the electric power of thepower generating unit to an external load on the basis of the voltage orcurrent-voltage characteristic measured by the characteristic-measuringmechanism.

Preferred embodiments of the invention will be described below whilereferring to the accompanying drawings. FIG. 1 shows a DMFC powergenerating device for use in the invention and a mechanical structuralexample thereof, and FIG. 2 shows a structural example of the DMFCsystem in an embodiment of the invention.

A power generating unit of a direct methanol fuel cell (DMFC) powergenerating device 100 comprises an anode electrode including an anodecurrent collector 101 and an anode catalyst layer 102, a cathodeelectrode including a cathode current collector 103 and a cathodecatalyst layer 104, and an electrolyte layer 105 provided between theanode electrode and the cathode electrode. An anode fluid channel plate106 is provided at the anode current collector 101 side, in which ananode fluid channel 109 having a methanol supply port 107 and a methanoldischarge port 108 is formed. A methanol aqueous solution container 110holding methanol aqueous solution is connected to the methanol supplyport 107 of the anode fluid channel plate 106 by way of a liquid supplypump 111. The power generating device 100 is heated by a heater (notshown).

On the other hand, a cathode fluid channel plate 112 is provided at thecathode current collector 103 side of the power generating device 100,in which a cathode fluid channel 115 having an oxidizer supply port 113and an oxidizer discharge port 114 is formed. An air supply pump 116 isconnected to the oxidizer supply port 113, and an oxidizer such as airis sent into the oxidizer supply port 113 from outside.

Methanol aqueous solution is supplied into the methanol supply port 107of the anode fluid channel plate 106 by the liquid supply pump 111 fromthe methanol aqueous solution container 110, and flows in the grooveportion of the fluid channel plate, that is, the anode fluid channel109. A convex portion of the anode fluid channel plate 106 is in contactwith the anode current collector 101 such as anode carbon paper. Whenthe methanol aqueous solution flowing in the anode fluid channel 109soaks into the anode current collector 101, the methanol aqueoussolution is supplied into the anode catalyst layer 102. However, all ofthe supplied methanol aqueous solution does not soak into the anodecurrent collector 101, but the remaining methanol aqueous solution isguided into the methanol aqueous solution container 110 from themethanol discharge port 108 by way of a fuel pipe 126.

On the other hand, the air taken in from the oxidizer supply port 113 bythe air supply pump 116 flows through a groove of the cathode fluidchannel plate 112, that is, the cathode fluid channel 115, and soaksinto the cathode catalyst layer 104. The remaining air is guided intothe methanol aqueous solution container 110 from the oxidizer dischargeport 114 by way of an exhaust pipe 127. Reference numeral 128 is a fuelcartridge, and when the methanol concentration in the methanol aqueoussolution container is lowered, for example, 98% concentration methanolis supplied from this cartridge.

Reference numeral 129 is a gas-liquid separation member, and evaporatessteam or the like out of components introduced into the methanol aqueoussolution container through the exhaust pipe 127. Reference numeral 130is a pressure regulating valve, which has a function of lowering theinternal pressure to about an atmospheric pressure when the internalpressure in the methanol aqueous solution container 110 is raised.

A film having a high proton conductivity, such as Nafion membrane, isused as the electrolyte layer 105. The catalyst used in the anodecatalyst layer 102 is, for example, PtRu of low toxicity, and Pt isused, for example, as the catalyst used in the cathode catalyst layer.

In the direct methanol fuel cell power generating device having suchstructure, methanol aqueous solution is supplied into the anode catalystlayer 102, protons are generated by catalytic reaction, and thegenerated protons pass through the electrolyte layer 105, and react withthe oxygen supplied in the cathode catalyst layer 104 on the catalyst,thereby generating electromotive force.

Referring next to FIG. 2, an embodiment of the invention is described.The DMFC system 200 mainly comprises a DMFC power generating device 100,a power generating unit 201 which supplies fuel and air into the DMFCpower generating device 100, an output unit 202 which checks an outputfrom the DMFC power generating device 100 and supplies to a load and asecondary battery, a power generation assist unit 203 which supplies thepower generation output, secondary battery output and external powersource output to a pump of the power generating unit, and an electriccontroller 204 which detects the voltage, current and temperature of theunits and controls the units electrically.

The power generating unit 201 comprises the DMFC power generating device100, a liquid supply pump 111 which supplies methanol in the methanolaqueous solution container 110 into the DMFC power generating device100, a motor 111 m which drives the liquid supply pump 111, an airsupply pump 116 which supplies external air into the DMFC powergenerating device 100, and a motor 116 m which drives the air supplypump. In the methanol aqueous solution container 110, methanol aqueoussolution of high concentration of predetermined concentration, forexample, concentration of 98% (95% or more and less than 100%) issupplied from the fuel cartridge 128, and a memory (EEPROM) 218described later is fixed to the outside of this fuel cartridge. Thememory stores therein various specifications such as the ID,concentration of the methanol aqueous solution contained herein, volumeof the container, and size of inlet and outlet.

An output unit 202 comprises a switch S21 connected to an outputterminal of the DMFC power generating device 100, an IV measuring unit206 that is connected between the other end of the switch and the groundand measures the current-voltage characteristic described later, aswitch S22 connected to one end of the IV measuring unit 206, electricpower output unit 207 connected to the other end of the switch S22, aSchottky barrier type diode D21 having its anode connected to the otherend of the same switch S22, a secondary battery charge controller 208having its input terminal connected to a cathode of the diode D21, aSchottky barrier type diode D22 having its anode connected to the outputterminal of the secondary battery charge controller 208 and its cathodeconnected to the output terminal of the electric power output unit 207,a switch S23 having one end connected to a cathode of this diode D22,and a capacitor C21 connected between the other end of the switch S23and the ground.

The IV measuring unit 206 comprises a resistor R21 connected between theswitch S21 and the switch S22, a resistor R20 connected in series to theground at the switch S22 side, and a switch S20. A variable resistor canbe used as the resistor 20. An example of variable resistor is shown inFIG. 11. Plural resistors 20 different in value are connected parallelto the resistor 21 and in a mutually exchangeable state. Each of theswitches S20 is connected in series to each of the resistors 20. Theother end of each switch 20 is grounded. The resistor R21 has a smallresistance which detects a current of, for example, tens of milliohms,and the resistor R20 has a resistance which is at least 10 times largerthan the resistance of the resistor R21.

When measuring the current-voltage characteristic, the switch S22 isturned off, and the corresponding switch S20 is sequentially turned onso as to change over the plural resistors R20. At this time, a voltagedrop is measured between the resistor R20 and resistor R21 correspondingto the switch S20 in ON state, or at both ends of the resistor 21, andthe current is calculated. The resistor R20 is changed by changing overthe switch S20, and when an electric current flows in the resistors R21,R20 and switch S20, the output voltage of the DMFC power generatingdevice 100 can be measured, and the current-voltage characteristic ismeasured. The output voltage of the DMFC power generating device 100 ismeasured by a voltage detector connected between the switch S21 and theground, as shown, for example, in FIG. 2. An output voltage may be alsoobtained by measuring the potential difference between the anodeterminal and the cathode terminal of the DMFC power generating device100.

On the other hand, the power generation assist unit 203 comprises aSchottky barrier type diode D24 having its cathode connected to thecathode of the diode D21 and its anode connected to an external powersource, a voltage adjusting unit which drives auxiliary machine 211having its input terminal connected to the cathode of the diode, aSchottky barrier type diode D25 having its cathode connected to theoutput terminal of the voltage adjusting unit for auxiliary machine 211,a switch S24 having its one end connected to the anode of the diode D25and its other end connected to the anode of the diode D22, a secondarybattery SB1 connected between the other end of the switch S24 and theground, a liquid supply pump drive unit 212 that has its input terminalconnected to the output terminal of the voltage adjusting unit forauxiliary machine 211 and moves the motor 111 m, and an air supply pumpdrive unit 213 that has its input terminal connected to the outputterminal of the voltage adjusting unit for auxiliary machine 211 andmoves the motor 116 m.

The electric power output unit 207, liquid supply pump drive unit 212,and air supply pump drive unit 213 comprises DC/DC converters.

The electric controller 204 comprises a voltage regulator 215 whichadjusts the voltage supplied from any one of the diodes D21, D24 andD25, a central processing unit (CPU) 215 a driven by the voltageregulator 215, an analog processing unit 216 which receives analogvalues of the current I and voltage V measured by the IV measuring unit206 and temperature T of methanol aqueous solution, and supplies theirdigital values into the CPU, a memory (EEPROM) 217 which stores variousdata and characteristic values, and a bus 219 which exchanges signalsamong the memory 217, CPU and memory (EEPROM) 218 that is attached tothe fuel cartridge 128. The memory 217 stores the amount of the methanolaqueous solution supplied from the liquid supply pump 111, the amount ofair supplied from the air supply pump 116, temperature, and othercontrol information. The bus 219 is I²C bus or SM bus, and parametersstored in the memories 217, 218 are transmitted to a host computerconnected to other end of the bus. The CPU and memory 218 may not beconnected by wire, but signals can be transmitted by wireless mechanismsuch as radio wave, light or electromagnetic coupling.

The analog processing unit 216 has a function of processing analogvalues of measured voltage (V), current (I) and temperature (T), andconverts these analog measured values into digital values, and suppliesinto the CPU 215 a. The temperature (T) inputted in the analogprocessing unit 216 is the temperature measured in the cell of the DMFCshown in FIG. 1, for example, the temperature of the separator at theposition of half number of the number of series unit cells. Because thisseparator is likely to achieve the highest temperature.

First, a starting operation of the system of the embodiment isexplained. Before start, all switches S21 to S24 are open (OFF state).When started as shown in step S501 in FIG. 5, the CPU 215 a controls theswitch S21 and switch S24 in step S502, and closes these switches (ONstate). When the switch S24 is closed, electric power is supplied fromthe secondary battery SB1 into the liquid supply pump drive unit 212 andair supply pump drive unit 213 by way of the diode D25. As a result, themotor 111 m and motor 116 m start operation, and the liquid supply pump111 and air supply pump 116 are put in operation (step S503).

The liquid supply pump 111 supplies the methanol aqueous solution ofpredetermined concentration in the methanol aqueous solution container110 into the methanol supply port 107 shown in FIG. 1 of the DMFC powergenerating device 100. The air supply pump 116 supplies external airinto the oxidizer supply port 113 shown in FIG. 1 of the DMFC powergenerating device 100. As the methanol aqueous solution flows in theanode fluid channel 109 and air flows in the cathode fluid channel 115,a chemical reaction takes place, and an electromotive force isgenerated.

As the electromotive force increases, the CPU 215 a detects that theoutput voltage of the DMFC power generating device 100 is heightened asthe input from the analog processing unit 216, and the IV measuring unit206 measures the current value flowing in the resistor R21 and thevoltage generated by this current (step S504). At this time, by changingover the resistor to change the resistance value from large to small,the current value changes from small to large, and by measuring thevoltage at this time, a current-voltage characteristic is obtained. Anexample of current-voltage characteristic obtained at this time is shownin FIG. 3.

In this diagram, reference numeral 31 is a current-voltagecharacteristic diagram, and 32 is a curve showing the electric power. Inthis electric power curve, unless the operation point is within therange of the initial value to maximum value, electric power cannot besupplied stably to an external load. Therefore, this current-voltagecharacteristic is investigated occasionally, and the current ismonitored such that the current of the output of the DMFC powergenerating device 100 may always settle within this range.

If the output current of the DMFC flows higher than this range only fora moment, the output voltage of the DMFC power generating device 100 maynot be reset, and therefore the switch S22 is turned off to change overso as to supply the electric power to the external load from thesecondary battery SB1 by way of the diode D22. In a predetermined time,the output voltage of the DMFC power generating device 100 is recovered,and hence by measuring the current-voltage characteristic again by theIV measuring unit 206, the switch S22 is turned on, and supply ofelectric power to the external load is changed over from the secondarybattery SB1 to the DMFC power generating device 100.

As the variable resistor contained in the IV measuring unit 206, forexample, a circuit as shown in FIG. 4A may be used. That is, the switchS25 is connected in series to the load (L1) including the resistor andinductor, and this switch S25 is controlled by the signal of the pulsewidth modulation (PWM) changing in width from large to small as shown inFIG. 4B. The resistor R21 is the same as the resistor R21 in FIG. 2.Instead of the load L1, a load which does not contain inductance may bealso used. At this time, by varying the resistance value of the load bya signal of pulse width modulation (PWM), the load can be used as avariable resistor.

As a result, the time width Wc of the conductive state of one period ischanged from small to large, and the time width Wo of cut-off state ischanged from large to small, thereby increasing the average current. Bymeasuring the voltage value when the current value is changed from smallto large, a current-voltage characteristic curve is obtained. Accordingto the IV measuring unit shown in FIG. 4A, it is advantageous that thecurrent-voltage characteristic can be obtained by a simple structure andin a short time.

Thus, by measuring the initial current-voltage characteristic curve,when the electromotive force of the DMFC power generating device 100increases, the CPU 215 a turns on the switch S22 (step S505). When theswitch S22 is turned on, electric power is supplied to the voltageadjusting unit for auxiliary machine 211, and the motors 111 m and 116 mare driven by the liquid supply pump drive unit 212 and air supply pumpdrive unit 213. Therefore, by the electromotive force of the DMFC powergenerating device 100, the liquid supply pump 111 and air supply pump116 are put in action (step S506). In the next step S507, the switch S24is turned off.

On the other hand, since the switch S24 is in the OFF state, electricpower is not supplied from the secondary battery SB1, and the secondarybattery charge controller 208 is operated through the diode D21, and thesecondary battery SB1 is charged.

When the electric power supplied from the electric power output unit 207becomes more than a predetermined value, the switch S23 is turned on(step S508), and the electric power induced in the DMFC power generatingdevice 100 is supplied to the external load, and a stationary state isestablished.

While supplying electric power to the external load, if the externalload suddenly becomes large, the output voltage may be lowered for ashort time, but in such a case, the electric power is supplied to theexternal load from the continuously-charged capacitor C21, so thatvoltage fluctuations can be suppressed. If the external load stays largelonger than the period estimated above, the diode D22 is put in actionto actuate the secondary battery SB1, so that the electric power is alsosupplied to the external load from this battery (S509).

When aforementioned stationary state continues, the methanol aqueoussolution supplied from the methanol aqueous solution container 110 intothe DMFC power generating device 100 decreases. Generally, consumptionof methanol is proportional to the current flowing in the small resistorR21, and its duration.

As shown in FIG. 1, when the remaining methanol aqueous solution isreturned from the fuel pipe 126 into the methanol aqueous solutioncontainer and recycled, the consumption of methanol is suppressed, butsince the methanol aqueous solution is consumed while flowing in theanode fluid channel, the methanol concentration in the methanol aqueoussolution container 110 is diluted. Accordingly, the fuel cartridge 128containing methanol aqueous solution at predetermined concentration isfitted to the fuel supply port of the methanol aqueous solutioncontainer 110, and methanol is supplied (step S510). At this time, fromthe memory 218 fixed to the fuel cartridge 128, various informationabout the fuel cartridge such as the ID, type and concentration ofmethanol aqueous solution, and aperture of inlet and outlet can betransmitted to the CPU by wired or wireless mechanism.

In this system, while generating power, the current-voltagecharacteristic is measured, for example, every hour or at a specifiedtime. That is, checking whether or not the predetermined time has passedin step S511, if passed, it is checked whether or not to terminate instep S512, and when not terminating, the current-voltage characteristicis measured again. This operation is explained. First, the switch S24 isturned on (step S513), and the liquid supply pump and air supply pumpare driven by the secondary battery SB1 (step S514).

In step S515, the switch S22 is turned off, and the current-voltagecharacteristic is measured. That is, after turning on the switch S20 ofthe IV measuring unit 206, the resistor R21 is changed over and varied,and the current-voltage characteristic shown in FIG. 3 is measured. Onthe other hand, electric power is supplied to the external load from thesecondary battery SB1 through the diode D22, and supply of electricpower to the external load is not stopped.

Since the current-voltage characteristic changes according to theconcentration of methanol aqueous solution supplied in the DMFC powergenerating device 100 and other circumstances, the measuredcurrent-voltage characteristic is different from the current-voltagecharacteristic measured upon start of power generation. In this DMFCsystem, however, without stopping the supply in the midst of supply ofelectric power to the external load, the current-voltage characteristicis measured regularly, so that the true electric power that can besupplied to the external load can be always known.

The terminating operation of the DMFC system of this embodiment isexplained. To terminate the system in step S512 in FIG. 5, the secondarybattery SB1 is fully charged in step S516. In next step S517, methanolaqueous solution is supplied from the fuel cartridge 128 so that themethanol concentration may be the initial concentration in the methanolaqueous solution container 110. After this process, the switch S24 isturned off and the liquid supply pump and air supply pump are stopped,and the DMFC system of this embodiment is stopped.

In case the secondary battery SB1 is not fully charged upon start ofthis DMFC system, electric power is supplied from outside through thediode D24, and the motors 111 m, 116 m are driven by the liquid supplypump drive unit 212 and air supply pump drive unit 213 by the auxiliarymachine driving voltage regulator 211, and methanol aqueous solution andair are set into the DMFC power generating device, and power isgenerated. As shown in FIG. 2, the cathodes of the diodes D21, D24, D25are connected to the voltage regulator 215, and electric power of theCPU 215 a is supplied from the voltage regulator 215, and therefore theCPU 215 a operates always from start till end of this DMFC system.

In this embodiment, the fuel cartridge 128 containing methanol aqueoussolution of high concentration of about 98% is connected to the methanolaqueous solution container 110, and this concentrated methanol aqueoussolution is supplied into the container. By using such a fuel cartridgecontaining methanol aqueous solution in high concentration, the fuelcartridge itself can be reduced in size. As the fuel cartridge, however,it is not always required to use a cartridge containing methanol aqueoussolution of a constant concentration and constant amount. Various fuelcartridges may be used, such as a large-sized fuel cartridge containinga large amount of methanol or methanol aqueous solution, or a cartridgecontaining methanol aqueous solution in relatively low concentration.

The concentration and amount of methanol aqueous solution are stored inthe memory 218 fixed to the fuel cartridge, and sent to the CPU or hostcomputer together with the information stored in the memory 217, and thesupply amount of methanol aqueous solution can be adjusted by the liquidsupply pump 111. Thus, by providing the fuel cartridge with the memory218 storing the parameters of the cartridge, fuel cartridges ofdifferent amounts or type may be used.

The information stored in the memory 218 fixed to the fuel cartridgeincludes a first information about the fuel cartridge and a secondinformation about the fuel stored in the fuel cartridge. And the mainpurposes of the information are prevention of accidents and detection ofremaining amount.

For the first information, the manufacturing date, number of times ofinsertion and extraction, ID, remaining amount, and failure flag arestored. The manufacturing date is to prevent liquid leakage andaccidental breakage, and aged tanks can be eliminated. The number oftimes of insertion and extraction is to check for deterioration of fuelsupply joint and to assure the reliability of electrical contact partsfor communication with information stored in the memory, and controlerrors due to liquid leakage or wrong information can be prevented. TheID is for eliminating pirated products (illegal copies), and preventingaccidents due to improper fuel. The memory of remaining amount is toprevent accidents in which power interruption of electronic componentsby shortage of fuel. The memory of failure flag is to detect the fueltank in which abnormality is detected to prevent its subsequent use,there by preventing accident.

The information about the fuel stored in the memory 218 includes theremaining amount information, full tank capacity, present amount andconcentration. From the memory of full tank capacity, the relativeremainder or consumption can be displayed, or the maximum driving timeis known when the fuel is replenished. When the present remaining amountis stored, the remaining driving time can be calculated. For example, itis known whether enough driving time is left or not for downloading ahuge amount of information, or it is determined whether a spare fuelcartridge is necessary or not. It is also possible to cooperate withsuspend, hibernation or resume function, and the application in actioncan be protected. Further, the weight of the fuel in the fuel cartridgecan be stored in the memory 218. And the number of times ofreplenishment can be stored when one replenishing amount from the fuelcartridge may be constant.

By storing the methanol concentration in the memory 218, a fuelcartridge of a different concentration can be used, and when operated ina high temperature climate, for example, a fuel of low concentration isused, or in a low temperature climate, a fuel cartridge containingmethanol aqueous solution of high concentration is used, and thus thefuel cartridges can be exchanged depending on the environments.

Similarly, by providing the system with the memory 217 storing datarelated to various parameters, the system itself can be replaced, and aflexible system can be built up.

A specific example of information stored in the memory 218 fixed to thefuel cartridge is described in detail. The memory 218 comprises a ROMregion in which the information is fixed at the time of shipping andcannot be changed, and a RAM region in which the information can berewritten during use, and each capacity is 0.5 k bits. Items stored inthe ROM region include the manufacturer's name, cartridge name,manufacturing date, maximum capacity of cartridge, fuel concentration,fuel type, maximum number of times of insertion and extraction, maximumliquid supply capacity, minimum operating temperature, maximum operatingtemperature, and spare items.

The manufacturer's name is, for example, the name registered in thestandardization society such as ASCII, and is assigned with a memorycapacity of 12 bytes for 16 characters. The cartridge name includes thetype name, manufacturing type number, product type number, and lotnumber, and is assigned with a memory capacity of 16 bytes for 16characters. The manufacturing date is mainly used for quality control,and a cartridge of an old manufacturing date is rejected, if installed,to prevent accident. The manufacturing date consists of 12 bits of year,4 bits of month, and 8 bits of day, and a total of 24 bits (3 bytes) isassigned as memory capacity. For example, if the manufacturing date is2000/12/31, it is 011111010000110000011111 in binary notation, and7d0c1f in hexadecimal notation. By assigning 3 bytes for this item, thedates can be stored to a maximum of 4095/12/31.

The cartridge maximum capacity refers to the maximum capacity of thefuel to be contained in the fuel cartridge. By assigning this item with4 bytes in the unit of microliter (μL), a capacity can be displayed in arange from 0 to 429,496,729 μL (about 429 liters). By specifying theitem of fuel concentration, a fuel cartridge of a differentconcentration can be used. In this item, by keeping 1 byte in the unitof 0.1 mol/L, the concentration can be displayed in a range of 0 to 25.0mol/L. By this item, since the maximum capacity of the fuel can bedetected, the remaining driving time or remaining electric power can bedetected by referring to the value of other item.

By the item of fuel type, for example, specifying 0 for water and 1 formethanol, other fuel than methanol can be also distinguished. Byassigning this item with 1 byte, up to 256 fuel types can bedistinguished from 0 to 255.

The maximum number of times of insertion and extraction can be changedepending on the structure of junction of fuel cartridge, therebyavoiding risk due to abnormally frequent insertion and extractionoperations. In the unit of number of times, when this item is assignedwith 2 bytes, the number of times of insertion and extraction can bepredetermined from 1 to 65,535 times, and when predetermined at 65,535,for example, it is assumed to be infinite. In the case of one-timedisposal fuel cartridge, this item is set at 1, and use of plural timesis prohibited to assure safety. The maximum liquid supply capacity isstored in consideration of the capacity of the liquid supply mechanismhaving a fuel tank. Assigning this time with 2 bytes, in the unit of 10μL/min, the maximum liquid supply capacity can be stored up to 655,350μL/min (about 0.65 L/min). In the case of a fuel tank without liquidsupply mechanism, this value is set at 0, and the type of the tank canbe determined by this value.

The minimum operating temperature can be predetermined in a range of 0to −128° C., for example, when 1 byte is assigned in the unit of degreecentigrade, and liquid supply failure due to freezing of fuel in thefuel cartridge can be prevented. The maximum operating temperature canbe predetermined in a range of 0 to 127° C., for example, when 1 byte isassigned in the unit of degree centigrade, and ignition or smoking offuel in the fuel cartridge can be prevented.

If a total of 64 bytes can be provided in the ROM region of the memory218, aside from these items, 17 bytes can be held of spare items. Amongspare items, for example, one bit may be used for parity check of theinformation of the items, and unauthorized alteration of items can bedetected. The spare item in the ROM region can be used, together withthe spare item in the RAM region, as information for distinguishing theID, pirated parts, etc.

The RAM region in the memory 218 stores, for example, the remaining fuelcapacity, number of times of insertion and extraction of fuel cartridge,duration of use, failure flag, and spare items. These items can berewritten when the fuel cartridge is inserted in or extracted from themethanol aqueous solution container.

The remaining capacity shows the remaining capacity of fuel at the timeof use, and is assigned with 4 bytes in the unit of microliters (μL),and the remaining capacity can be stored in a range of 0 to4,294,967,295 μL (about 429 liters). In the mechanism of the fuel cell,if only the number of times of fuel supplying is counted, the controlmicrocomputer converts the count value into the consumption of fuel, andby subtracting from the cartridge maximum capacity stored in the ROMregion or the value of this item stored before use, the remainingcapacity can be calculated, and this value is stored again as the valueof this item. The value of the remaining capacity can be expressed alsoin percentage as relative capacity, by referring to the cartridgemaximum capacity stored in the ROM region.

When the fuel cartridge is replenished with fuel, the remaining capacityvalue is updated by adding the replenishing amount. By this function, anarbitrary amount of fuel can be added. When filling with fuel by apredetermined replenishing device, the remaining capacity of the deviceis read from the memory, and the replenishing amount and remainingcapacity can be calculated and stored accurately. If replenished withfuel illegally, the memory content is not updated and the remainingcapacity becomes 0, and therefore illegal use can be prevented andstable action can be maintained.

The number of times of inserted and extracting the fuel cartridge isstored, and when this value reaches the maximum number of times ofinsertion and extraction stored in the ROM, the corresponding fuelcartridge cannot be used any longer. The number of times of insertionand extraction is counted by adding +1 by the control microcomputerevery time the fuel cartridge is extracted and inserted. The unit ofthis time is the number of times, and by assigning with 2 bytes, thenumber of times of insertion and extraction can be stored in a range of0 to 65,535 times, and the maximum value of 65,535 may be set to beinfinite. When the maximum value is set to 65,535, the fuel cartridgecan be recycled many times.

The operation time is the cumulative time of the fuel cartridgeinstalled in the DMFC power generating device, and judges and displaysthe exchange of the fuel cartridge by the fuel microcomputer from thetemperature history, state of use, manufacturing date, fuel temperatureand fuel type. When this item is assigned with 4 bytes, for example, inthe units of hours (h), the operation time can be stored for a maximumof 65,535 h (about 7 and a half years). The fuel cartridge may berecycled, but by determining the upper limit (maximum operation time) ofthe operation time and storing in the ROM region, the limit of therecycling cartridge may be determined by comparing this value with theoperation time.

The failure flag item stores the history of various abnormal states.When this item is assigned with 8 bytes, a maximum of 64 bits, that is,64 types of abnormal state can be stored. As an abnormal state, forexample, if the fuel methanol is not delivered by operating the fuelcell, or an abnormal amount of fuel is delivered, it can be stored as aspecific bit of a failure flag. Since the fuel stored in the fuelcartridge is usually a methanol aqueous solution of high concentration,storage of history of this failure flag is very important from theviewpoint of safety. When a capacity of 64 bytes is assured in the RAMregion, the remaining 46 bytes can be used for the spare items.

In this embodiment, all items above are stored in the memory 218 fixedto the fuel cartridge 128. However, in the methanol aqueous solutioncontainer 110, too, a memory such as an EEPROM can be fixed. Thus, whena memory is installed in the methanol aqueous solution container 110, itis also divided into the ROM region and RAM region, and all of theseitems, or specific items such as container manufacturing date, maximumliquid supply capacity, and operation time may be stored in the memory.By installing the memory also in the methanol aqueous solution containerand storing the attributes of the container, it is easier to replace themethanol aqueous solution container itself.

In this embodiment, the methanol aqueous solution not reacted in theDMFC power generating unit, and water, steam and carbon dioxide passingthrough the cathode passage are all returned to the methanol aqueoussolution container, and methanol is supplied from the fuel cartridge.However, this is not always necessary in the invention. For example, asshown in FIG. 6A, a fuel cartridge 61 containing spare methanol aqueoussolution and a methanol aqueous solution container 62 are integrallycomposed, and when supplying methanol aqueous solution into the DMFCpower generating device, spare methanol aqueous solution is put into thecontainer 62, or as shown in FIG. 6B, the methanol aqueous solution leftover in the DMFC power generating device 63 is returned to a methanolaqueous solution container 64, and water and steam generated by chemicalreaction during power generation are condensed by a condenser 66, andonly water can be returned to the fuel cartridge 65 and methanol aqueoussolution container 64. Further, such a fuel cartridge 65 can beintegrated with the methanol aqueous solution container 64.

In the explanation of the embodiment, electric memories are used, butany other memories may be used as long as the information can be stored,and the information may be stored in a magnetic recording medium, orstored by mechanical method such as punching, notching or marking, andsuch mechanical memories are also included as memories in the invention.

In the invention, to start the pump in the first place, a secondarybattery is used, and by using the secondary battery, when electric poweris supplied to the load from the power generating device, it can becharged, and the time until independent charging can be extended.However, in the invention, the battery is not limited to the secondarybattery, and generally any auxiliary battery may be used until asufficient power is generated by the power generating unit.

Other aspects of the invention are a direct methanol fuel cell systemcomprising a power generating unit including an anode electrode, acathode electrode, and an electrolyte layer provided between the anodeelectrode and the cathode electrode, a fuel tank for storing a fuelcontaining methanol to be supplied to the anode electrode, and a fuelcartridge including a spare fuel tank for storing the fuel to bereplenished in the fuel tank, and a harmful substance trap member forcapturing harmful substance in the gas in the fuel tank.

An embodiment of the direct methanol fuel cell (DMFC) system in anotheraspect of the invention is explained by referring to FIG. 7 to FIG. 9.In FIG. 7 to FIG. 9, the same members as explained in FIG. 1 areidentified with the same reference numerals, and a duplicate explanationis omitted.

This DMFC system further comprises a cathode recovery container 131.This cathode recovery container 131 is connected to a cathode piping132, and is also connected to a methanol aqueous solution container 110by way of a cathode piping 132. The cathode piping 132 has a check valve133 to prevent counterflow of the liquid in the cathode recoverycontainer 131.

In the cathode recovery container 131, water is contained before startof power generation, and the exhaust pipe 127 is connected below theliquid level, and hence the gas exhausted from the cathode electrode isbubbled in water. From the cathode electrode, unreacted methanol, water,air, carbon dioxide, formaldehyde, and formic acid are discharged, andpart of formaldehyde and formic acid are bubbled and dissolved in thewater in the cathode recovery container 131. The water in which thecathode product is dissolved is collected in the methanol aqueoussolution container 110 from the cathode recovery container 131 by way ofthe piping 132. Along with the recovery, the gas in the cathode recoverycontainer 131 is also sent into the methanol aqueous solution container110.

The gas-liquid separator 129 is fixed, for example, in the inner wall ofthe methanol aqueous solution container 110. The gas-liquid separator129 is formed of porous material such as nonwoven fabric. The gas-liquidseparator 129 passes only the gas collected in the methanol aqueoussolution container 110.

A second fuel cartridge 136 includes a spare fuel tank 134 and a harmfulsubstance trap member 135 externally attached to the spare fuel tank134. The second fuel cartridge 136 is detachably connected to themethanol aqueous solution container 110. In the spare fuel tank 134,methanol aqueous solution is contained. The methanol concentration ofthe methanol aqueous solution in the spare fuel tank 134 is preferred tobe higher than the methanol concentration of the methanol aqueoussolution in the methanol aqueous solution container 110, andspecifically in a range of 95% or more to less than 100%. The spare fueltank 134 is connected to the methanol aqueous solution container 110 byway of a liquid supply pipe 137. When the methanol concentration of themethanol aqueous solution in the methanol aqueous solution container 110is diluted, methanol aqueous solution is supplied from the spare fueltank 134, and the methanol concentration of the methanol aqueoussolution in the methanol aqueous solution container 110 can bemaintained at a constant value.

The harmful substance trap member 135 is connected to the gas-liquidseparator 129 by way of an air supply pipe 138. An example of theharmful substance trap member 135 is explained by referring to FIG. 8and FIG. 9.

The harmful substance trap member 135 includes a trap material container140 (made of resin such as acrylic plate) having a gas exhaust port 139.In the trap material container 140, a gas pipe (gas diffusion passage)142 having a gas inlet port 141 is provided. The gas pipe 142 is made ofresin such as acrylic plate, and has a meandering shape. To prevent thegas exhausted from the gas-liquid separator 129 from being releasedoutside through the gas exhaust port 139 directly without diffusing inthe harmful substance trap material, the terminal end of the gas pipe142 does not communicate with the gas exhaust port 139. In the gas pipe142, as shown in FIG. 9, plural gas diffusion holes 143 are opened. Aharmful substance trap material 144 fills up the gap between the innerwall of the trap material container 140 and the outer wall of the gaspipe 142. The harmful substance trap material 144 contains at least onepowder of active carbon and silica gel. In particular, active carbon ispreferred. This is because many functional groups such as hydroxyl groupand carboxyl group are present on the surface of the active carbon, andorganic substances such as formaldehyde and formic acid can be trappedeasily.

By the harmful substance trap member 135 having such structure, the gaspassing through the gas-liquid separator 129 is introduced into the gaspipe 142 from the gas inlet port 141 through the air supply pipe 138,and is diffused into the harmful substance trap material 144 from thegas diffusion holes 143. Organic substances such as formaldehyde andformic acid are easily adsorbed on the active carbon of the harmfulsubstance trap material 144. As a result, harmful substances such asformaldehyde and formic acid can be removed from the exhaust gas. Theexhaust gas being rid of harmful substances is released outside throughthe gas exhaust port 139.

When methanol aqueous solution is used up in the spare fuel tank 134 ofthe second fuel cartridge 136, it is replaced with a new fuel cartridge,and in this fuel cartridge, a sufficient amount of fuel is contained inthe spare fuel tank, and the harmful substance trap member 135 isreplenished with unadsorbed harmful substance trap material 144, so thatthe harmful substance trap member 135 can be always maintained in theharmful substance adsorbing state by replacing the fuel cartridge. As aresult, release of harmful substance to outside from the fuel cellsystem can be avoided, and the impact on the environment is reduced, andsafety for the human body may be enhanced.

The replenishing amount of the harmful substance trap material 144 ispreferred to be set so that the trap material 144 may be break throughwhen the methanol aqueous solution is nearly used up in the spare fueltank 134. As a result, the wasteful amount of the trap material 144 maybe kept to a minimum, and the adsorption capacity of the trap material144 may be maintained during the operation of the DMFC system.

In FIG. 8, a meandering pipe is used as the gas pipe 142, but the pipeshape is not particularly limited as long as the gas diffusion speedinto the harmful substance trap material 144 may be enhanced. Forexample, as shown in FIG. 10, two or more branch pipes 146 may beconnected to a main piping 145 having a gas inlet port 141. Gasdiffusion holes are preferred to be opened in the pipings 145, 146 asshown in FIG. 9. To prevent the gas exhausted from the gas-liquidseparator 129 from releasing outside from the gas exhaust port 139without diffusing in the harmful substance trap material 144, theterminal ends of the pipings 145, 146 do not communicate with the gasdischarge port 139.

On the outer surface of the spare fuel tank 134 of the second fuelcartridge 136 or on the outer surface of the trap material container 140of the harmful substance trap member 135, the memory (EEPROM) 218 can befixed. By recording the parameters having the harmful substance trapmaterial 144 (such as trap member replenishing amount) in the memory218, in addition to the parameters of the spare fuel tank 134,replacement of fuel cartridge can be indicated at the timing of breakingthrough the harmful substance trap material 144.

Examples of the invention are described in detail below while referringto the accompanying drawings.

Example 1 Fabrication of Anode Electrode

Perfluorocarbon sulfonic acid solution and ion exchange water were addedto carbon black carrying catalyst for anode (Pt: Ru=1:1), and thiscatalyst carrying carbon black was dispersed, and paste was prepared.The paste was applied on carbon paper with water repellent treatment asanode current collector, and dried to form an anode catalyst layer, andan anode electrode was obtained.

<Fabrication of Cathode Electrode>

Perfluorocarbon sulfonic acid solution and ion exchange water were addedto carbon black carrying catalyst for cathode (Pt), and this catalystcarrying carbon black was dispersed, and paste was prepared. The pastewas applied on carbon paper with water repellent treatment as cathodecurrent collector, and dried to form a cathode catalyst layer, and acathode electrode was obtained.

<Preparation of Membrane-Electrode Assembly (MEA)>

A perfluorocarbon sulfonic acid membrane was arranged as electrolytemembrane between the anode catalyst layer of anode electrode and thecathode catalyst layer of cathode electrode, and by applying hot press,the anode electrode, electrolyte membrane and cathode electrode werejoined, and a membrane-electrode assembly was obtained.

<Fabrication of Harmful Substance Trap Member>

A trap material container of acrylic resin having a structure as shownin FIG. 8 was prepared. The space between the inner wall of thecontainer and the outer wall of the gas pipe was replenished with activecarbon as a harmful substance trap material, and a harmful substancetrap member was obtained.

Using the obtained membrane-electrode assembly and harmful substancetrap member, a direct fuel cell system having a structure as shown inFIG. 7 was assembled.

Example 2

A direct fuel cell system having the same structure as in example 1 wasassembled except that silica gel was used as the harmful substance trapmaterial.

In the direct fuel cell systems of example 1 and example 2, methanolaqueous solution was supplied in the anode electrode, air was suppliedin the cathode electrode, and a load current of 150 mA/cm² was appliedfor 1 hour while keeping the power generating unit at 70° C., and avoltage of about 0.4 V was obtained. During this operation, theconcentration of formaldehyde and formic acid released from the gasexhaust port 139 of the harmful substance gas trap member 135 wasmeasured, and a removal rate of over 95% was obtained in both example 1and example 2 (as compared with the concentration before introductioninto the gas trap member 135).

According to the invention, the current-voltage characteristic of theelectric power generated in the power generating unit is measured, andthe supply of electric power to the external load is controlledaccording to this characteristic, electric power can be supplied to theload stably for a long period, and therefore a practical direct methanolfuel cell system is obtained.

The invention also presents a direct methanol fuel cell system and fuelcartridge having less load on environments.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A direct methanol fuel cell system comprising: a power generatingunit including an anode electrode, a cathode electrode, and anelectrolyte layer provided between the anode electrode and the cathodeelectrode; a fuel tank which stores a first liquid fuel containingmethanol to be supplied to the anode electrode; and a fuel cartridgecomprising a spare fuel tank which stores a second liquid fuel forreplenishment in the fuel tank which contains methanol, and a harmfulsubstance trap member which is fixed to the spare fuel tank and containsa harmful substance trap material which traps a gaseous harmfulsubstance exhausted from the fuel tank.
 2. The direct methanol fuel cellsystem of claim 1, further comprising a memory which is fixed to thespare fuel tank, and stores at least one of information about the sparefuel tank and information about the second liquid fuel.
 3. The directmethanol fuel cell system of claim 1, wherein the harmful substance trapmember includes a trap material container having a gas exhaust port, agas diffusion passage which is formed in the trap material container,and a gas diffusion hole opened in a wall of the gas diffusion passage,and the harmful substance trap material is filled in a space between aninner side of the trap material container and a wall of the gasdiffusion passage.
 4. The direct methanol fuel cell system of claim 1,wherein the first liquid fuel is a methanol aqueous solution.
 5. Thedirect methanol fuel cell system of claim 1, wherein the second liquidfuel is a methanol aqueous solution having a concentration of a range of95% or more to less than 100%.
 6. The direct methanol fuel cell systemof claim 1, wherein the first liquid fuel is a methanol aqueous solutionand the second liquid fuel is a methanol aqueous solution whoseconcentration is higher than that of the first liquid fuel.
 7. Thedirect methanol fuel cell system of claim 1, wherein the harmfulsubstance trap material includes at least one powder of active carbonand silica gel.
 8. The direct methanol fuel cell system of claim 1,wherein the harmful substance trap material includes active carbon.